Bluetooth connectivity has become a common feature in many electronic devices, including a wide array of both OEM and aftermarket head units. Once you experience the ease of use and wireless convenience a Bluetooth connection provides, it's hard to imagine living without it.

Bluetooth isn't only for making phones calls anymore. There is much more you can do, including streaming music from your phone directly to your head unit and, now with Pandora internet radio, you can take your favorite music via personalized Pandora stations with you wherever you go.

To bring this technology to the masses, Alpine has developed a new single-DIN HD radio/Bluetooth/Pandora/CD/MP3 player called the CDE-HD137BT. The unit sells for $219.95 in the U.S. and comes with a bunch of other cool features too. Alpine has graciously provided one for testing.

FEATURESWhenever I review a product as cool as the CDE-HD137BT, I can't help but feel a bit sorry for my Canadian friends who don't have full access to what I think is some of the coolest technology to come along in the car audio world this decade. I'm talking, of course, about HD radio and Pandora internet radio. My Canuck friends, you don't know what you're missing.

With HD radio you're able to receive special digitally broadcast stations that aren't available to regular analog radio listeners. HD radio provides ID3 tags for artist and song information and allows tagging of songs so you can download them later via iTunes. In addition, the HD radio service allows you to bookmark things for retrieval later, pause live radio and, if your head unit is also a GPS unit, provide real-time traffic updates. Best of all, it's free. All you need is a HD radio receiver.

Then there's my favorite feature of this unit: the Pandora internet radio connection for Android and/or Blackberry smartphone users. I'm a Blackberry guy and I've been using Pandora for about two years. If you haven't used Pandora yet, you need to check it out.

Pandora internet radio allows you to create your own stations based on your own musical tastes and preferences. I have stations for hard rock, jazz, classic rock, folk/bluegrass/country, rockabilly/blues and even a comedy station. Whatever my mood, I just pick my appropriate Pandora station and it plays what I want to hear!

With Alpine's CDE-HD137BT, you have full access to all of the above and much more! The unit plays back CD/MP3/WMA/AAC formats and boasts full iPod/iPhone compatibility, USB and auxiliary inputs. Bluetooth allows hands-free phone calls complete with a call waiting function and the unit ships with a mic. For crystal clear sound quality, there are five settings to choose from. You also have the ability to adjust mic gain, phone level and ring volumes.

The audio section is loaded with features as well, like a three-band parametric type EQ with four selectable frequencies per band, adjustable Q and level. There are also easy-to-select preset EQ curves for those who don't fancy themselves as tweakers. For those who do enjoy dialling in their systems, there are high- and low-pass crossovers with variable frequencies, loudness contour, the ability to turn off the internal amp for maximum preout performance as well as subwoofer phase and level settings too.

Compatible with virtually any type of USB-based flash memory, portable music player and Bluetooth phone, the CDE-HD137BT provides a vast array of choices when it comes to how and what you want to connect to it.

CONTROLS & ERGONOMICSI like the layout and controls of the CDE-HD137BT very much. The removable faceplate incorporates a volume knob that is a good size and a pleasure to use with or without gloves. Small positive-feeling detents provide good feedback for adjustments without looking. The source/power button is large and easily accessed with gloved hands; and, the track up/down buttons on the top edge of the control panel are easily found by touch only.

The white on dark blue LCD panel is easy to read and can be adjusted to display a variety of information. The phone and audio buttons are also large enough to access quickly and placed well for easy access. The USB port is hidden behind a small door on the front of the unit and stays hidden when not in use. This unit feels intuitive and doesn't require a long glance away from the road to find a commonly-used control. Well done Alpine!

Making the audio tuning adjustments is almost as easy once you understand the navigation of the unit's menus. I especially appreciate the amount of time users are given to make adjustments before the screen defaults back to the source. This simple feature allows you to adjust and listen, then adjust again without the hassle of always having to walk through the menu each time.

The CDE-HD137BT comes with an 18-watt four-channel amplifier, a fairly large heatsink on the back of the radio and its own cooling fan. If you need more power in a quick and easy format, the unit is compatible with Alpine's plug-and-play KTP-445 Power Pack. Preamp outputs for front, rear and sub are found on the rear panel along with connections for the microphone and optional third-party steering wheel control adaptor.

LISTENINGThis is 2012 and we've come to expect great sound from any major brand of head unit and, in this regard, the Alpine certainly doesn't disappoint. Regardless of the source, the sound quality is excellent and there is no audible noise from the unit in any mode. Combined with the built-in EQ and crossover functions, its sound quality and tuning capability will satisfy all but the pickiest of tuners. For these folks, Alpine offers other models with even greater tuning functionality.

Pairing the unit with my Blackberry is dead simple and, thanks to Alpine's “Bluetooth Plus” technology, I didn't even have to enter a code to pair it. Once paired, I select the “BT Pandora” source and within seconds the music from my station is playing with all the clarity and musicality Pandora has become famous for. It couldn't be any simpler: no fuss, no mistakes, no resetting anything, I don't even need to read the manual. This is what I mean by intuitive.

Alpine has been a recognized leader when it comes to interfacing with an iPod – and the CDE-HD137BT's connection with my overloaded device is fast and easy-to-use. Naturally, the head unit will keep your iPod/iPhone charged while connected unless, of course, you're like me and leave the wires at home to take full advantage of the Bluetooth connectivity.

PERFORMANCE / BENCH MEASUREMENTSAfter I'm done listening and messing around, I bring the unit over to my test bench for a thorough examination and evaluation. The unit performs with excellence in all regards and my measured performance data exceeds all of the published specs. The built-in amp delivers 19.2 watts minimum per channel with all channels driven into four ohms. The preamp section produces 2.2 volts of usable output voltage with a respectable output impedance of 128 ohms. Signal-to-noise performance is exceptionally good and frequency response also excellent. If you are looking for more output voltage, as I mentioned earlier, Alpine has a higher performance four volt model just for you.

CONCLUSIONNot too long ago it was almost inconceivable a car audio head unit could have the ability to receive digital radio broadcasts, allow hands-free telephony, playback music from a USB drive, control and charge an iPod, let alone stream music from our own personal internet radio stations! But, now the Alpine CDE-HD137BT allows all that and more for under $220 bucks!

If you have a Bluetooth-enabled smartphone and are a Pandora user, this unit is made for you. Check it out at a dealer near you or online at www.alpine-usa.com. For more info on HD radio or Pandora internet radio, visit www.hdradio.com and www.pandora.com.